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Voters in Alabama, California, Iowa, Mississippi, Montana, New Jersey, New Mexico and South Dakota headed to the polls Tuesday, the biggest flurry of activity yet in an already contentious primary season.

The Golden State is at the center of the action where competitive primaries and the state's "jungle primary" system have combined to create a uniquely challenging set of circumstances for both parties.

California's "top two" primary system where candidates of all parties compete against each other on one ballot has created the prospect of Democratic lockouts in key U.S. House seats up and down the state in districts they'll need to win in November if they want to make their dream of retaking the chamber a reality.

Gavin Newsom|U.S. Senate|House of Representatives

From left, Gavin Newsom, Dianne Feinstein and Dana Rohrabacher.

Other marquee races included a liberal challenge to longtime Democratic incumbent Sen. Dianne Feinstein and a crowded field of high-profile Californians hoping to become the next governor of the nation's largest state.

Key races in the other seven states voting Tuesday included the GOP primary to see who will take on Democratic incumbent Sen. Jon Tester, Democratic primaries in several New Jersey U.S. House districts that will be key to the party's hopes of recapturing the majority in Congress' lower chamber, and a governors race in New Mexico that will likely feature two sitting members of Congress.

Polls closed in California at 11 pm EST, in Iowa and Montana at 10 pm EST, in New Mexico and South Dakota at 9 pm EST, and in Alabama, Mississippi and New Jersey at 8 pm EST.

2:00 a.m. - California governor, Montana U.S. Senate races set, key House races in the Golden State still undecided

Two of 2018's most high profile statewide races are set after Tuesday.

California Lieutenant Governor Gavin Newsom will take on businessman John Cox in the race to be the Golden State's next governor.

"The halftime score is looking very promising and the home team is winning big,” Newsom said to a crowd of a few hundred supporters.

In Montana, Democratic Sen. Jon Tester will take on Republican State Auditor Matt Rosendale in what promises to be one of Novembers' marquee races.

Elsewhere in California, the outlook of several races key to Democratic hopes of retaking the U.S. House in November remains murky.

Of the seven districts in California that Hillary Clinton won in the 2016 election, just one has a projected Democratic winner as of 2 a.m. EST (T.J. Cox, who ran unopposed in the state's 21st Congressional District).

12:17 p.m. - Newsom advances to November in California governors race

California Lieutenant Gov. Gavin Newsom has advanced to the November general election in the race to be the next chief executive of the Golden State, the Associated Press projected.

Newsom, the former Mayor of San Francisco, is leading the primary field with over 34 percent of the vote.

Republican John Cox, who has the endorsement of President Trump, is currently in second place, which would secure him a spot on the November ballot against Newsom.

Democratic congressional candidate Deb Haaland is the winner of the Democratic primary in New Mexico's 1st Congressional District, an open seat race with current Rep. Michelle Lujan Grisham running for governor.

The Associated Press projected Haaland the winner just after 11:40 p.m. EST.

If elected in November, Haaland would be the nation's first Native American woman elected to Congress.

“Tonight, New Mexico made history," Haaland wrote in a statement late Tuesday night, "Thank you to the tens of thousands of volunteers, grassroots donors, and supporters who won this election today. I’m honored and humbled by your support. Our win is a victory for working people, a victory for women, and a victory for everyone who has been sidelined by the billionaire class."

Polls have now closed in the most populous state in the union, California.

Competitive primaries for governor, U.S. Senate and a slew of U.S. House races, including seven GOP-held district Hillary Clinton won in the 2016 election, put California at the center of the action tonight.

The state's 'jungle primary' system has created headaches for both parties, and crowded races up and down the state have them fearing they could have zero candidates on the November ballot in several districts.

Still looming over results in the state is the situation in Los Angeles County, where over 100,000 voters names were not listed on polling place rosters due to a printing error.

The California Secretary of State had no comment when asked by ABC News' Alex Stone if they plan to keep polling places in the county open past 11 p.m. EST, which was requested by gubernatorial candidate Antonio Villaraigosa, the former mayor of Los Angeles.

I'm calling on @LACountyRRCC to keep the polls open longer because of the unprecedented number of voters left off the voter rolls. You have the right to vote. If you were turned away, return to your polling place & exercise your right to vote by requesting a provisional ballot. pic.twitter.com/hLxVPaa9ML

In Alabama, incumbent GOP Rep. Martha Roby is heading to a July runoff election with Bobby Bright, one of her Republican primary challengers and a former Democratic Member of Congress, the Associated Press projected. Thus far this cycle only one sitting member of Congress, Republican Robert Pittenger of North Carolina, has lost in a primary.

In New Mexico, it will be congressman versus congresswoman, as Democratic Rep. Michelle Lujan Grisham advanced and will take on GOP Rep. Steve Pearce in November.

In Montana, Democratic Senator Jon Tester advanced to the November general election but is still awaiting his GOP opponent. The Republican race is a tight two-man race between Russ Fagg, a local judge, and Matt Rosendale, the State Auditor of Montana. The Associated Press has not yet projected the GOP race.

GOP Rep. Greg Gianforte, who holds the state's lone congressional seat, also advanced, and will take on one of six Democrats vying to replace him. The Associated Press has not yet projected the Democratic primary for U.S. House.

Campaign manager Addisu Demissie knows his candidate has a big lead in the polls, but no one is popping the champagne until the first results come in.

After a campaign stop this afternoon in Oakland, Newsom has spent the rest of the day with his family. His campaign manager says he spent time with his dad, and will put his young kids to sleep before joining his watch party in a few hours.

Former California state senator Kevin de Leon is mounting a primary challenge to longtime Democratic Sen. Dianne Feinstein, trying to take advantage of a crowded primary that may not see a Republican advance to the November ballot.

10:05 p.m. - FiveThirtyEight on the importance of the Asian-American vote in California

More from our friends at FiveThirtyEight:

We’re about an hour away from polls closing in California, which has one of the most diverse in the country. One group that’s drawn recent attention from both parties is Asian-Americans – a segment of the electorate that is diverse in its own right, encompassing multiple national and linguistic backgrounds, and including recently naturalized citizens as well as those whose families have been in the U.S. for generations.

There are a few things that are interesting to watch:

One is that, as with other groups that have historically been marginalized, there are a number of Asian-American candidates running for office in 2018.

Additionally, this demographic group has been somewhat of a political enigma. A 2016 survey showed that 2 in 5 Asian American voters didn’t identify with either the Democratic or Republican parties. (Here’s some data about partisan identification among white, black and Latino voters for comparison.)

Political scientists have studied how to mobilize Asian American voters. Perhaps most intriguingly, Ph.D. candidate Sara Sadhwani found that these voters in key California districts (39, 48) supported Republican House candidates in 2016, but cast their presidential ballots for Hillary Clinton. In a year with “no purple states,” that makes this set of voters interesting to parties and to political analysts.

10:00 p.m. - Polls close in Iowa, Montana

Polls have closed in the Iowa and Montana.

In Montana, the key race to watch is the GOP primary for U.S. Senate, which will determine incumbent Democratic Sen. Jon Tester's opponent in November. Tester is one of ten sitting Democratic senators up for re-election in states that Donald Trump won in the 2016 presidential election.

The gubernatorial race in Iowa, as well as the race in the state's 1st Congressional District, are both expected to be competitive in November.

The Democratic gubernatorial primary in Iowa will determine who takes on sitting GOP Gov. Kim Reynolds, who took over the office after former Gov. Terry Branstad was appointed the United States Ambassador to China.

9:45 p.m. - Projections made in New Jersey, Mississippi U.S. Senate races

In New Jersey, the Associated Press projected that incumbent Democratic Sen. Bob Menendez has won the Democratic primary for U.S. Senate over Lisa McCormick, a little-known challenger.

Justin Sullivan/Getty Images

Democratic California gubernatorial candidate Lt. Gov. Gavin Newsom with his children and his wife, Jennifer Siebel Newsom sign in to vote at the Masonic Temple Fairfax on June 5, 2018 in Larkspur, California.

Republican pharmaceutical executive Bob Hugin, who poses a well-funded challenge to Menendez in November, won the nomination for U.S. Senate, the Associated Press also projected.

In other notable New Jersey news, former Navy pilot and assistant U.S. attorney Mikie Sherrill is the projected winner in the 11th district Democratic primary. Democrats have identified the 11th as a prime pickup opportunity with Rep. Rodney Frelinghuysen retiring.

And former assistant secretary of state Tom Malinowski is the projected winner in the 7th Congressional District's Democratic primary – one of ABC News' "18 for '18" races.

Julio Cortez/AP

U.S. Sen. Bob Menendez exits a polling booth after casting his vote in the New Jersey primary election, June 5, 2018, at the Harrison Community Center in Harrison, N.J.

In Mississippi incumbent GOP Sen. Roger Wicker won the GOP primary, the Associated Press projected. The Associated Press has not yet projected who Wicker's Democratic opponent will be.

9:15 p.m. - FiveThirtyEight highlights five Democrats and five Republicans to watch tonight

FiveThirtyEight has highlighted some key Democrats and Republicans to watch as they emerge from tonight's primaries.

Five Republicans To Watch:

U.S. Rep. Kristi Noem of South Dakota is locked in a competitive Republican primary for an open seat for governor. She’s one of a handful of congresswomen who has opted to run for higher office rather than seek re-election, which could add to the ranks of women governors and senators — or could just leave a dearth of Republican women in Congress.

In the same vein, South Dakota Secretary of State Shantel Krebs is the only woman running in the primary to replace Noem in the House.

John Cox won’t be California’s next governor, but he could help Republicans keep their majority in Congress if he finishes in the top two in the state’s gubernatorial primary. California Republicans don’t have a competitive Senate candidate, but a Republican at the top of the ballot in the governor’s race could help ensure GOP turnout doesn’t dip, particularly in Orange County, where Republicans are defending several seats in districts that Hillary Clinton carried in 2016. Having Cox at the top of the ticket would also be a solace to a state Republican Party that has had a rough go of late and retain some presence for the party on the West Coast generally.

Democrats could be locked out of the general election in one of those districts if former state Assemblyman Scott Baugh finishes second in the primary to incumbent GOP Rep. Dana Rohrabacher in the 48th District. OK, a Baugh vs. Rohrabacher race doesn’t really fall along any important GOP fault lines, but still … it would be interesting.

And in Alabama’s 2nd District, U.S. Rep. Martha Roby faces a primary against Roy Moore’s former Senate campaign manager and a former Democratic congressman. Roby, who drew the challenge in large part because she criticized Trump, could be the second GOP member to lose renomination this cycle. And her fate may be a sign of how loyalty to Trump will figure in the GOP’s future.

Five Democrats To Watch Tonight

In Iowa, state Rep. Abby Finkenauer is the front-runner to face GOP Rep. Rod Blum this November in the state’s 1st Congressional District, which Trump carried with less than 50 percent in 2016. Finkenauer’s profile, as a 28-year-old from Dubuque with support from local labor unions, fits what some Democrats believe is the future of the party.

In New Jersey, state Sen. Jeff Van Drew is running for an open seat in New Jersey’s 2nd District, easily outpacing his primary opponents in fundraising. But a previous “A” rating and contribution from the National Rifle Association has drawn criticism, including from Parkland, Florida, shooting survivor David Hogg on Twitter.

In California, pediatrician Mai Khanh Tran is running against a lottery winner and insurance executive in the state’s 39th District. Democrats in Washington aren’t particularly excited about Tran, but if she finishes in the top two, it would show the limits of the DCCC’s intervention and the power of being the only credible woman candidate in a crowded field.

New Mexico Rep. Michelle Lujan Grisham is the only woman in the Democratic race to succeed Republican Gov. Susana Martinez. Inside Elections rates the race as “Lean Democratic.”

Also, in New Mexico — if former state party chair Deb Haaland wins the primary for Lujan Grisham’s House seat, she could be the first Native American woman to serve in Congress.

Rouda is a Democrat running in the crowded primary in California's 48th Congressional District, currently represented by GOP incumbent Rep. Dana Rohrabacher, who is facing a primary challenger from within his own party in former state Assemblyman Scott Baugh.

Polls have closed in both New Mexico and South Dakota, two states holding gubernatorial elections this cycle.

In New Mexico, the race will likely be between two members of Congress -- Democrat Michelle Lujan Grisham and Republican Steve Pearce.

Since Lujan Grisham and Pearce are both running for governor, two of New Mexico's three congressional seats, the 1st and 2nd districts, are open seat races this year, and primaries on both sides are crowded and worth watching.

In South Dakota, GOP Rep. Kristi Noem is up against the state's Attorney General Marty Jackley. South Dakota state senator Billie Sutton is running unopposed for the Democratic nomination in the gubernatorial race.

8:45 p.m. – Over 100,000 Los Angeles County voters left off polling place rosters

The polls don’t close in California for over two hours, but some voters are already dealing with a major snafu on Election Day.

According to ABC affiliate KABC, thousands of voters in Los Angeles County arrived at their designated polling places Tuesday only to find that their names were not on the list.

The Los Angeles County Registrar-Recorder's Office says that the issue was brought to officials' attention and poll workers are tracking the occurrences. The error stems from an apparent "random drop off" during the printing of the rosters, according to officials.

A total of 1,530 voting locations were affected, and 118,522 voters' names were omitted from the lists, officials confirmed in a press release.

8:20 p.m. - In California's battleground districts, Republicans take lead in mail-in ballots

Turnout is key for both Democrats and Republicans in the three battleground congressional races in Southern California – and all candidates will tell you every single vote matters in a crowded race under a "jungle" primary system, ABC News’ Esther Castillejo reports.

Polls don't close until 8 PM PST, but if early turnout data is any indication, both parties have a long night ahead of them in Orange County.

Democrats and no-party-preference independents may be gaining grounds on the Party of Lincoln in California, but Republicans are still the party with the most registered voters in Orange County – and many appear to be heeding the call to vote early.

According to data compiled by Politics Data, Inc., a group collecting voter registration and turnout across the state, of the 202,869 by-mail ballots that have been returned in the 39th, 48th and 49th Congressional Districts here, 42.8 percent are Republican so far, compared to 36.21 percent of Democrat ballots returned.

Voters who haven't mailed in their ballots can still drop them off at polling locations across the districts, and candidates until late today were reminding voters they could do so.

8:00 p.m. - Polls close in Alabama, Mississippi and New Jersey

Polls have closed in two southern states, Alabama and Mississippi, and the state of New Jersey.

The Garden State is key to Democratic hopes of retaking the U.S. House in 2018.

Rogelio V. Solis/AP

Madison County election bailiff Shirley Lewis unrolls several "I Voted" stickers that they give to each person who votes in their respective party in the Mississippi primary, June 5, 2018, in Madison, Miss.

The retirements of two Republican congressmen, Frank LoBiondo and Rodney Frelinghuysen, are two seats Democrats are eager to flip in November.

Few races in Alabama or Mississippi are expected to be competitive in November, but one race to keep an eye on is Alabama's 2nd Congressional District, where incumbent GOP Rep. Martha Roby is facing a crowded Republican primary, and may have to win a runoff election in July if she does not receive over 50 percent of the vote tonight.

It's 4 p.m. in California, just a few hours before polls close, and in some corners of the 39th Congressional District, voters are still undecided.

That's one of the main takeaways from all the calls Democratic candidate Sam Jammal has made here today. Just now, there was a man who told him he's voting in a half hour and wasn't sure who to vote for.

Julio Cortez/AP

A sign announces in Spanish, a polling place outside of the Harrison Community Center in Harrison during New Jersey primary election, June 5, 2018, in Harrison, N.J.

"I'm trying to have that last personal touch with voters to make my case to them," he told ABC News' Esther Castillejo.

The personal touch includes his personal number – his cell phone ringing mid-conversation.

"Every vote matters, this is going to be a tight race I think for both parties, and it's largely because of the fact that we have so many candidates running that a lot of voters are still undecided," he said.

There are 18 people on the ballot in this district, all first-time candidates. While not all of them have been actively campaigning, it's fallen on the campaigns to educate voters. Incumbent Republican Ed Royce, who has represented the district for nearly 25 years, is not seeking re-election.

On the army of people running? Jammal sees it as mostly a positive thing, especially for Democrats looking to make ground in this traditionally Republican enclave in California.

"Obviously it would be easier from a personal standpoint if there were fewer candidates, but from the standpoint of we do need to build our infrastructure here as Democrats, I don't think it's a bad thing," he said.

4:15 p.m. - Catch up on all the key races at stake on Tuesday

California may be the key state to watch Tuesday, but primaries in seven other states across the country promise to provide crucial clues for both parties' hopes in the coming November midterms.

U.S. Senate

Jon Tester.

From Montana to Iowa, New Jersey to New Mexico, primary voters will decide consequential races up and down the ballot Tuesday.

Last month, the city of Costa Mesa became the latest in a growing number of cities south of Los Angeles in the Orange County, to officially oppose the state’s California Values Act. The state law expands protections for undocumented immigrants by preventing, in many cases, local law enforcement from holding people at the request of federal immigration agents. The law also limits some information sharing between local law enforcement and federal immigration agents about select inmates.

Michael Anaya Gorman

Deb Haaland is on the Democratic ballot in the June 5 primaries for New Mexico's 1st Congressional District. If she wins her party's nominee and wins in the general election, she'll become the country's first ever Native American congresswoman.

The local branch of the American Civil Liberties Union describes the law as designed so "no state or local resources are diverted to fuel any attempt by the federal government to carry out mass deportations."

Half a dozen local governments in the Orange County area have taken legal action against the state over the issue.

Some 47 percent of all registered voters in South Dakota are Republicans, and in raw numbers, they outnumber Democrats by nearly 100,000 voters according to registration data from the secretary of state.

But the political fundamentals of the state have not deterred Democratic state senator Billie Sutton from mounting an aggressive campaign to be its next governor.

Sutton, who was paralyzed from the waist down in a professional rodeo accident in 2007, is running as a moderate Democrat hoping to capitalize on what he believes is a hunger among South Dakota voters for a unifying figure.

"I’m sure there are some views that I hold that Republicans might not like. There are some views I hold that Democrats might not like. But at the end of the day the important thing to remember is we have more in common than not, regardless of party affiliation," Sutton told ABC News ahead of Tuesday's primaries in South Dakota, where he is running unopposed for the Democratic nomination.

ABC News' John Verhovek reports

2:15 p.m. - New Mexico Democrat hopes to be nation's first Native American woman in Congress

But if she wins in the 1st Congressional District Democratic primary election Tuesday, she might be able to change that, for herself and for Native American women across the country.

House of Represetatives

Leonard Lance.

“In 230 years, there’s never been a Native American woman in Congress. I have never seen myself in that body of our government,” Haaland said in an interview with ABC News. There are currently two Native American representatives in the House — both men from Oklahoma.

Unfortunately, that lived experience can turn into a self-fulfilling prophecy for some. “Ten years ago, when I was out in Indian country knocking on doors and driving folks to the polls, I never thought I would run for Congress,” Haaland acknowledged. But eventually, a desire to serve her community lead her to politics.

Haaland is running for the seat left open by Democratic Rep. Michelle Lujan Grisham, who is now running for governor.

California’s once-touted “jungle primary” - which will be featured in the marquee races on Tuesday, when voters in seven states go to the polls - is following its own unusual laws. Foremost on that list is the rule of good intentions leading to unintended consequences, ABC News Political Director Rick Kleinwrites.

It’s a simple concept: Under the law approved by 54 percent of California voters in 2010, the top two vote-getters, regardless of party affiliation, will advance to the general election in every race in California.

House of Representatives

Devin Nunes.

Instead of Democrats and Republicans each choosing one candidate in separate primaries, the final two in each race could include two Democrats, two Republicans, one of each, or even one or two third-party candidates.

While this system has been in place in California since 2012, and while Louisiana and Washington state, have roughly similar ways of choosing candidates, it has never mattered like it could in 2018. This year, it could conceivably sway the balance of power in Washington.

Rather than tempering partisanship, it has sparked fierce intra-party warfare.

1:30 p.m. - Steady stream of voters in the city of Yorba Linda, California

It is 10:30 a.m. in California and a steady stream of voters - young and old - are making their way into a polling station here in the city of Yorba Linda, in California’s 39th congressional district, ABC News' Esther Castillejo reports.

A line — something uncommon here in a midterm primary election, and not seen since the district voted for Hillary Clinton for president and Ed Royce for Congress in 2016 — is forming just outside the room where just over a half dozen booths are set up for people to vote.

When the line is short, the whole process is done in an instant. But right now, the line is not short — and the “instant” process is taking closer to 15 minutes, as voters trickle in and out.

“All the people who didn’t vote last time are voting today,” said the polling station’s greeter, as a young voter asked for a sticker to show she voted before walking out into the overcast summer day.

Turnout will be key in this race. Here, 17 candidates are jockeying for one of the two spots on the November ballot, after Royce announced he’d decided not to seek re-election.

12:25 p.m. - In an attempt to retake the House, Democrats target a number of New Jersey House seats

New Jersey is a state where Democrats control both chambers of the statehouse and where the party has dominated in presidential elections ranging back to 1992. It spent eight years under the leadership of moderate Republican Gov. Chris Christie, but voters' embrace of Murphy's liberal campaign platform – which included calls for marijuana legalization and a $15 minimum wage – appeared to be a harbinger of a shift left for the already blue state.

Mike Nelson/EPA via Shutterstock

Voters mark their ballot at the Santa Monica City Hall polling station as Californians turned out for the state's primary elections, June 5, 2018.

As a result, Democrats, who already hold seven of the state's 12 congressional seats, are optimistic that they can dominate November's slate and push their number of representatives into double digits. The impending retirement of two New Jersey Republican congressmen has only served to increase Democrats' focus on the midterms.

ABC News' Adam Kelsey reports.

11:30 a.m. - Feinstein faces a challenger from the left

The top Democratic challenger to Sen. Dianne Feinstein, D-Calif., has raised concerns that she doesn’t fully grasp the depth of Californians’ opposition to President Donald Trump.

Former California state senator Kevin de León is waging an aggressive challenge to Feinstein and is hoping to earn a spot on the November ballot over more than a dozen Republicans who filed to run for the U.S. Senate.

Kevin de Leon

Kevin de Leon.

But other close watchers of the race say those interactions reinforced Feinstein’s reputation with California voters as a lawmaker who will represent their desires and, with senior perches on the Senate Judiciary, Intelligence and Appropriations Committees, someone with serious pull in Washington. Add to that the fact that she has the level of high name recognition that comes with 26 years in the office and her campaign’s war chest and she’s a tough candidate to beat.

“The idea that she’s not effective, influential and perfectly prepared to do this job is belied by everything we’ve seen in the last few months,” Bob Shrum, a longtime Democratic strategist and a political science professor at the University of Southern California, told ABC News.

ABC News' Ali Rogin reports.

9:02 a.m. - President Trump weighs in on key California primaries

President Trump took to Twitter Tuesday morning, urging voters to back a slew of candidates in various California races for governor and the U.S. House.

Trump also tweeted support for incumbent Mississippi Republican Sen. Roger Wicker, who is not facing a significant primary challenger. The real action in Mississippi is in the fight for the state's other U.S. Senate seat - where there is no primary election and appointed Sen. Cindy Hyde-Smith faces a November special election.

In High Tax, High Crime California, be sure to get out and vote for Republican John Cox for Governor. He will make a BIG difference!

If there’s such a thing as too much of a good thing in politics, we’re about to find out — courtesy of the state that’s the de facto headquarters of “the resistance," ABC News Political Director Rick Kleinwrites in ABC's morning political newsletter.

Democrats’ biggest threat to a California sweep – which itself could be vital to hopes for a blue wave - comes not from President Donald Trump but from Democrats themselves.

Blame the state’s unusual all-party “jungle primary” system, or blame Democratic leaders for not being able to sort out intramural fights, or for not knowing enough about all the candidates running and what it all would mean. Either way, there are simply too many Democrats running for too few competitive seats going into Tuesday’s primary.

WATCH LIVE TUESDAY: You can watch livestreaming coverage of all the primary action starting Tuesday at 10 PM Eastern/7 PM Pacific on ABCNews.com or on the ABC News app available on the Apple App Store, Google Play Store, Apple TV App Store, and Roku Channel Store.

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